WO2021241542A1 - Core-shell particle, composite, light-receiving member for photoelectric conversion element, and photoelectric conversion element - Google Patents

Abstract

A core-shell particle (10) has a core-shell structure comprising an inorganic nanoparticle (11) having a light wavelength conversion ability and a coating layer (12) formed on the surface of the inorganic nanoparticle (11) and composed of an inorganic perovskite-type substance.

Description

Core-shell particles, complexes, light-receiving members for photoelectric conversion elements, and photoelectric conversion elements

The present invention relates to core-shell particles, a composite, a light receiving member for a photoelectric conversion element, and a photoelectric conversion element. The present application claims priority based on Japanese Patent Application No. 2020-093726 filed in Japan on May 28, 2020, the contents of which are incorporated herein by reference.

Photoelectric conversion elements such as solar cells and photodiodes are widely used in various fields. However, the conventional photoelectric conversion element has a problem that the detection sensitivity is weaker than the light in the visible light region with respect to the light in the near infrared region. If the detection sensitivity of light in the near-infrared region can be increased in the same manner as visible light, for example, in a solar cell, the photoelectric conversion efficiency can be improved.

Patent Document 1 discloses a technique using up-conversion nanoparticles as an inorganic porous material for supporting an organic-inorganic composite perovskite-type compound which is a power generation layer. Here, the up-conversion nanoparticles refer to particles having a particle size on the order of nm, which has a function of converting long-wavelength light such as infrared rays into short-wavelength light such as visible light and ultraviolet rays. This technology converts long-wavelength light such as near-infrared light absorbed by inorganic core-shell particles into short-wavelength light such as visible light and ultraviolet light, and reabsorbs this into organic-inorganic composite perovskite crystals. It excites energy and generates electromotive force.

In Non-Patent Document 1, inorganic nanoparticles (Lantande-dropped NPS) and inorganic perovskite quantum dots (CaPbX ₃ (X = Cl, Br, I) PeQDs) are mixed in a state of being separated from each other, and the inorganic nanoparticles are nano-sized. A technique utilizing the particle up-conversion function is disclosed. In this technique, visible light generated by near-infrared light excitation by inorganic nanoparticles is reabsorbed by inorganic perovskite quantum dots and emitted.

Japanese Patent Application Laid-Open No. 2015-92563

In the configuration disclosed in the above document, energy loss is unavoidable when the light after wavelength conversion is reabsorbed by the perovskite. Therefore, when the light to be absorbed is weak, sufficient electromotive force or light emission is generated. Is difficult.

In conventional up-conversion nanoparticles containing rare earth ions, the concentration of ions responsible for light emission needs to be about 1 to 5%, and when the concentration of ions responsible for light emission is increased, the light emission is extinguished. This is because under high concentration conditions, cross-relaxation occurs between the luminescent species, and the energy is deactivated by the thermal vibration of the chain-like organic molecules coated on the surface of the nanoparticles. Therefore, the amount of light absorption is very small, and up-conversion does not occur unless the light is strong.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to make it possible to obtain high visible light sensitizing characteristics by using weak light having a long wavelength.

In order to solve the above problems, the present invention provides core-shell particles, a composite, a light receiving member for a photoelectric conversion element, and a photoelectric conversion element. The present invention employs the following means.

(1) The core-shell particles according to one aspect of the present invention include inorganic nanoparticles having a wavelength conversion ability of light and a coating layer formed on the surface of the inorganic nanoparticles and made of an inorganic perovskite-type substance. Has a structure.

(2) In the core-shell particles according to (1), it is preferable that the inorganic nanoparticles contain a rare earth element.

(3) The complex according to one aspect of the present invention is an aggregate or a thin film containing a perovskite structure as a main component and further containing the core-shell particles according to any one of (1) and (2) above.

(4) The light receiving member for a photoelectric conversion element according to one aspect of the present invention is a coagulation containing a layer composed of the composite according to (3) above and an organic or inorganic semiconductor (including a metal complex) as a main component. It is made by laminating a layer composed of an aggregate or a thin film.

(5) The photoelectric conversion element according to one aspect of the present invention includes the light receiving member for the photoelectric conversion element according to (4) above between the hole transport layer and the electron transport layer.

(6) The photoelectric conversion element according to one aspect of the present invention is formed on the surface of a first layer composed of a plurality of particles containing an inorganic semiconductor as a main component, an aggregate thereof, or a thin film, and the surface of the first layer. A second layer composed of the composite according to claim 3 and a third layer composed of a plurality of particles containing an organic or inorganic semiconductor (including a metal complex) as a main component or an aggregate or a thin film thereof. In the conduction band, the energy level of the second layer is higher than the energy level of the first layer, and the energy level of the third layer is higher than the energy level of the second layer. ..

(7) In the photoelectric conversion element according to (6), the third layer contains an organometallic complex as a main component, and the energy level of the second layer in the valence band is the energy level of the third layer. It may be higher than the rank.

According to the present invention, the dopant concentration of a luminescent species, which was conventionally several%, can be increased to 100% by forming a perovskite coating layer on the surface. As a result, high visible light sensitization characteristics can be obtained by using weak light with a long wavelength.

According to the present invention, there are provided a core shell particle, a composite, a light receiving member for a photoelectric conversion element, and a photoelectric conversion element capable of obtaining high visible light sensitizing characteristics by using weak light having a long wavelength. Can be done.

It is sectional drawing of the core shell particle which concerns on one Embodiment of this invention. It is sectional drawing of the photoelectric conversion element provided with the core-shell particles of FIG. The structure of the energy band of each layer during the operation of the photoelectric conversion element of FIG. 2 is shown. It is sectional drawing of the modification of the photoelectric conversion element provided with the core-shell particles of FIG. The structure of the energy band of each layer during the operation of the photoelectric conversion element of FIG. 4 is shown. It is sectional drawing of the object to be processed in the manufacturing process of the photoelectric conversion element of FIG. It is a graph which shows the emission spectrum of a core- shell particle 1, 2 and a nanoparticle 1. It is a graph which shows the change of the absorption rate by the difference in the structure of the core-shell particles of the second layer. It is an SEM image of the cross section of the photoelectric conversion element manufactured as Example 2. It is a graph which shows the spectrum of the light emission generated after absorbing the wavelength-converted light in the second layer of the photoelectric conversion element of Example 2. FIG. It is a graph which shows the response speed of the photocurrent obtained in the photoelectric conversion element.

Hereinafter, the core-shell particles, the composite, the light receiving member for the photoelectric conversion element, and the photoelectric conversion element according to the embodiment to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following explanation, in order to make the features easy to understand, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. No. Further, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

(Core shell particles)
FIG. 1 is a cross-sectional view schematically showing the configuration of core-shell particles 10 according to an embodiment of the present invention. The core-shell particles 10 mainly include inorganic nanoparticles 11 and a coating layer 12 thereof, and have a core-shell structure.

The inorganic nanoparticles 11 are particles having a particle size (diameter) 11a of about 10 nm to 100 nm and have a wavelength conversion ability of light. The wavelength conversion ability of light here means the ability to convert the wavelength of incident light and emit light having a wavelength different from that of incident light. In the present embodiment, a case where the incident near-infrared light is emitted as visible light after its wavelength is converted will be described by way of an example.

The main materials of the inorganic nanoparticles 11 include, for example, erbium (Er), thulium (Tm), ytterbium (Yb), neodymium (Nd), formium (Ho), placeodium (Pr), gadrinium (Gd), and europium ( Examples thereof include rare earth elements such as Eu), terbium (Tb), thulium (Sm), and cerium (Ce), or those containing at least one of these compounds.

The coating layer 12 is formed on the surface of the inorganic nanoparticles 11 and is made of an inorganic perovskite type substance. Since the surface of the up-conversion nanoparticles of a general rare earth element is coated with a plurality of chain-like organic molecules (oleylamine, oleic acid, etc.), the emission of light emission occurs through the thermal vibration of the chain-like organic molecules. .. On the other hand, in the core-shell particles 10 of the present disclosure, since the coating layer 12 covers the surface of the inorganic nanoparticles 11, there is no thermal vibration of chain organic substances (Organic liquid) unlike general up-conversion nanoparticles. Dissipation of light emission via thermal vibration can be suppressed. The coverage of the coating layer 12 on the surface of the inorganic nanoparticles 11 may be approximately 50% or more, preferably 100%.

The thickness 12a of the coating layer 12 may be 5% or more of the particle size 11a of the inorganic nanoparticles, and is preferably substantially uniform over the surface of the inorganic nanoparticles. The thicker the thickness 12a of the coating layer 12, the higher the photoelectric conversion efficiency.

Examples of the material of the inorganic perovskite-type substance constituting the coating layer 12 include a composite composed of three kinds of inorganic elements, for example, CsPbX _{3 and the} like (X = Cl ⁻ , Br ⁻ , I ⁻ ). X contains at least one of the halogen ions. _{For example, when ErYF 4} or Er, Yb-doped NaYF ₄ (NaYF4: Er, Yb) is used as the inorganic nanoparticles 11, it is preferable _{to use CsPbBr 3} or CsPbI _{3 because the} photoelectric conversion efficiency is improved. When Tm, Yb-doped NaYF ₄ (NaYF4: Tm, Yb) is used, it is preferable to use CsPbCl _{3 because the} photoelectric conversion efficiency is improved.

FIG. 1 (b) shows a modified example of the core-shell particle 10 shown in FIG. 1 (a). As shown in FIG. 1B, the covering layer 12 may be formed by stacking two layers, or may be formed by forming three or more layers.

(Photoelectric conversion element)
FIG. 2A is a cross-sectional view of the photoelectric conversion element 100 provided with the core-shell particles 10. The photoelectric conversion element 100 is mainly composed of a positive electrode layer (positive electrode member) 101, a negative electrode layer (negative electrode member) 102, and a photoelectric conversion layer 103 sandwiched between them.

Between the negative electrode layer 102 and the photoelectric conversion layer 103, E _cb is used as the energy level of the conduction band, and between _{E c2} and E _c3 as the energy level of the conduction band between the negative electrode layer 102 and the photoelectric conversion layer 103. The buffer layer 107 having (that is, E _c2 <E _cb <E _c3 ) may be sandwiched between the two. Examples of the constituent material of the buffer layer 107 include europium oxide (Eu ₂ O ₃ ), titanium oxide, tin oxide and the like.

In order to take light into the photoelectric conversion layer 103, the negative electrode layer 102 is made of a light-transmitting material such as antimony-doped indium oxide (ATO), indium tin oxide (ITO), zinc oxide, tin oxide, and fluorine-doped indium oxide (ATO). It is preferable that it is composed of FTO) or the like. Since it is necessary to perform heat treatment in the manufacturing process of the photoelectric conversion layer 103 of the present embodiment, ATO having heat resistance is preferable as the material of the negative electrode layer 102.

The positive electrode layer 101 does not have to be transparent, and a metal, a conductive polymer, or the like can be used as the electrode material of the electrode. Specific examples of the electrode material include metals such as gold (Au), silver (Ag), aluminum (Al), and zinc (Zn), and two or more alloys thereof, graphite, graphite interlayer compounds, polyaniline and the like. Examples include derivatives, polythiophene and derivatives thereof. Examples of the material of the transparent positive electrode layer 101 include ITO.

As shown in FIG. 2A, the photoelectric conversion layer 103 is mainly composed of a plurality of particles (hereinafter, also referred to as “particles of an inorganic semiconductor”) 20 containing an inorganic semiconductor as a main component. A second layer 105 having a first layer 104a, formed on the surface of the first layer 104a, containing a perovskite structure as a main component, and further composed of an aggregate or a thin film (complex) containing core-shell particles 10. , A third layer 106 composed of a plurality of particles containing an organic or inorganic semiconductor (including a metal complex) as a main component, an aggregate thereof, or a thin film may be laminated. That is, the photoelectric conversion element 100 is arranged in the order of the positive electrode layer 101, the third layer 106, the second layer 105, the first layer 104, and the negative electrode layer 102, and at least a current path from the positive electrode layer 101 to the negative electrode layer 102 is formed. It should be configured so as to. Here, "containing an inorganic semiconductor as a main component" means that the inorganic semiconductor contains an amount capable of exhibiting the function of the present invention in the particles 20 of the inorganic semiconductor, and specifically, for example, an inorganic. It means that the content of the semiconductor is more than 50% by volume. It is preferably more than 90% by volume, and more preferably substantially composed of an inorganic semiconductor. "Containing a perovskite structure as a main component" means that the perovskite structure contains an amount capable of exerting the function in the present invention with respect to the total mass of the second layer 105, specifically, for example. , The content of the perovskite structure is more than 50% by volume. It is preferably 70% by volume or more. Further, "containing an organic or inorganic semiconductor (including a metal complex) as a main component" means that an aggregate or a thin film (composite) containing the core-shell particles 10 has a function in the present invention with respect to the total mass of the third layer 106. It means that the content of the aggregate or the thin film (complex) containing the core-shell particles 10 is more than 50% by mass. It is preferably more than 90% by volume, and more preferably substantially composed of an organic or inorganic semiconductor (including a metal complex). The larger the number of current paths formed, the more preferable, but the adjacent current paths may or may not be electrically connected to each other. The "layer" in the present embodiment means a film formed by one or a plurality of film forming processes, and is not limited to a flat film and may not be integrated. It shall be.

Further, regarding the materials and compositions of the three layers 104 to 106, the energy level of the conduction band (LUMO, excited state) is increased in the order of the first layer 104, the second layer 105, and the third layer 106. It is determined. For example, for the first layer 104, the energy level of the valence band can be -8 eV or more, and the energy level of the conduction band can be -4 eV or less. At this time, for the second layer 105, the energy level of the valence band can be set to −6.0 eV or more, and the energy level of the conduction band can be set to -3 eV or less. Further, for the third layer 106, the energy level of the conduction band is preferably -2 eV or less.

The first layer 104a is an aggregate of a plurality of inorganic semiconductor particles 20 formed on the negative electrode layer 102, and is a porous film having a plurality of voids between the particles 20 of the inorganic semiconductor. The particles 20 of the inorganic semiconductor in contact with the second layer 105 are in direct contact with the negative electrode layer 102 or indirectly via the particles 20 of another inorganic semiconductor so as to be electrically connected to the negative electrode layer 102. ing.

The inorganic semiconductor contained in the particles 20 of the inorganic semiconductor preferably has an absorption wavelength in the ultraviolet light region, and examples thereof include titanium oxide and zinc oxide. The thickness of the first layer 104 is preferably about 10 nm or more and 1000 nm or less, and more preferably about 50 nm or more and 500 nm or less.

The second layer 105 is a thin film that covers an exposed portion of the surface of the inorganic semiconductor particles 20 at the manufacturing stage, that is, a portion that is not in contact with either the negative electrode layer 102 or the inorganic semiconductor particles 20. The second layer 105 does not need to cover the entire exposed portion, but must cover at least the positive electrode layer 101 side in order to form the current path.

Perovskite structure constituting the second layer ^105, Pb ^{2+, Sn} 2+, etc. of the metal ^cation, I ^-, Cl ^-, halide anions such as ^{_{Br-, CH 3 NH 3 + (}} MA), NH = CHNH 2 + It is composed of a plurality of molecules composed of organic cations such as (FA) and C _s ^+. The size and shape of the bandgap can be changed depending on the number of ions selected from each of the metal cation, the halide anion, and the organic cation. When tin is added to the perovskite structure, the bandgap is narrowed and the responsiveness to long wavelength light such as near infrared light can be improved, but it is easily oxidized in the atmosphere and the characteristics are deteriorated. In each molecule constituting the perovskite structure, the halogenated anion is arranged at the apex of the octahedron centered on the metal ion, and the organic cation is located near the cube containing the metal ion centered on the metal ion. It is arranged. Specifically, a regular octahedron formed of metal ions and halogenated anions forms a three-dimensional lattice, and the structure is such that organic cations enter the gaps.

When the core-shell particles 10 form the second layer 105 while being in contact with the perovskite structure, the boundary between the coating layer 12 and the perovskite structure in the core-shell particles 10 disappears. Therefore, the light converted into visible light by the core-shell particles 10 is efficiently absorbed by the perovskite structure including the coating layer 12. This makes it possible to improve the detection sensitivity of light in the near infrared region of the photoelectric conversion element 100.

When the core-shell particles 10 in the second layer 105 are 5 wt% or more, the sensitivity of light in the near infrared region is improved, which is preferable. If the core-shell particles 10 in the second layer 105 are more than 30 wt%, it becomes difficult to form a perovskite structure, so 30 wt% or less is preferable.

Further, it is preferable that the energy level of the valence band of the second layer 105 is lower than the energy level of the valence band of the third layer 106 and is intermittently connected to the same energy rank. Examples of the composition of the second layer 105 (perovskite structure) satisfying these conditions include CH ₃ NH ₃ Pbl ₃ , NH = CHNH ₂ PbI ₃ , and CsPbI ₃ . In addition to this, among the halide anions, those having different composition ratios of I and Cl or Br can be mentioned.

The third layer 106 may be a thin film that covers the surface (exposed surface) of the perovskite structure contained in the second layer among the photoelectric conversion element precursors composed of the first layer 104 and the second layer 105. .. The third layer 106 is formed of any of a p-type organic semiconductor, an inorganic semiconductor, and an organometallic complex. FIG. 2A shows an example of an organometallic complex, where 106A in FIG. 2A represents an inorganic transition metal ion of the third layer 106 and 106B represents an organic ligand of the third layer 106. .. The thickness of the third layer 106 is preferably, for example, 1 nm or more and 100 nm or less.

Examples of the p-type organic semiconductor constituting the third layer include bathocuproine (BCP), 2,2', 7,7'-tetrakis (N, N'-di-p-methoxyphenyllamine) -9,9'-spirobifluorene (Spiro). -OMeTAD), poly (3,4-ethylendioxythyophene): poly (styrenesulfonate) (PEDOT: PSS), N, N, N', N'-tetracis (4-methoxyphenyl) -benzidine (TPD) and the like.

Examples of the p-type inorganic semiconductor constituting the third layer include CuI and CuSCN.

When the photoelectric conversion element 100 of the present embodiment is applied to an optical sensor or a photovoltaic element (solar cell), the photoelectric conversion element 100 is mounted on a semiconductor substrate such as silicon or a glass substrate. In this case, for example, the following device configurations can be mentioned. (1) The transparent positive electrode layer 101 is formed on the uppermost layer farthest from the semiconductor substrate (that is, from the uppermost layer on the light receiving side, the (transparent) positive electrode layer 101 / third layer 106 /. Second layer 105 / first layer 104 / negative electrode layer 102 / (Si) substrate in that order)
(2) The transparent negative electrode layer 102 is formed so as to be adjacent to the glass substrate (that is, from the uppermost layer on the light receiving side, the (glass) substrate / negative electrode layer 102 / first layer 104 /. (Structure in which the second layer 105 / third layer 106 / positive electrode layer 101 are laminated in this order)
(3) The transparent negative electrode layer 102 is formed on the uppermost layer farthest from the semiconductor substrate (that is, from the uppermost layer on the light receiving side, the (transparent) negative electrode layer 102 / first layer 104 /. Second layer 105 / third layer 106 / positive electrode layer 101 / (Si) substrate in that order)

(Energy band structure)
3 (a) to 3 (c) show the structure of the energy band of each layer during the operation of the photoelectric conversion element 100 according to the present embodiment.

In the non-irradiated state, the energy level of the conduction band of the third layer 106 is higher on the positive electrode layer 101 side than the Fermi level of the positive electrode layer 101, as shown in FIG. 3 (a). , The current from the positive electrode layer 101 to the negative electrode layer 102 is blocked.

When the photoelectric conversion element is irradiated with light having a wavelength of 800 nm or more, the core (inorganic nanoparticles 11) of the core-shell particles 10 constituting the second layer 105 absorbs the light and converts the wavelength into visible light. .. The perovskite structure absorbs the wavelength-converted light (FIG. 3 (b)). The broken line arrow and the solid line arrow of the core-shell particle 10 in FIG. 3B indicate energies of the same magnitude. By absorbing light, the perovskite structure generates electrons e and holes h, the electrons e _{move to the conduction band E c1} , and the holes h _{move to the valence band E v3} (FIG. 3 (c)).

In the above example, the case where the first layer 104a is a porous film has been described as an example, but the first layer is formed in a uniform film shape as in the first layer 104b of FIG. 2 (b). You may.

(Modification example of photoelectric conversion element)
Next, a modification of the photoelectric conversion element will be described. Hereinafter, similar components are distinguished by adding different alphabets after the same code. However, the description of the same component will be omitted. Further, among similar components, when they have substantially the same functional configuration as the components described, the description of the components will be omitted.

FIG. 4A is a cross-sectional view of the photoelectric conversion element 100b provided with the core-shell particles 10. The photoelectric conversion element 100b is mainly composed of a positive electrode layer (positive electrode member) 101, a negative electrode layer (negative electrode member) 102, and a photoelectric conversion layer 103b sandwiched between them. Note that FIG. 4A is a cross-sectional view showing a detailed structure, but in some cases, it may be simply described as shown in FIG. 4B. Incidentally, in FIG. 4B, among the configurations of the photoelectric conversion layer 103c, the second layer 105c and the third layer 106c are shown as layers facing the negative electrode layer 102 (and the buffer layer 107) and the positive electrode layer 101c. There is. A simple description of the photoelectric conversion layer 103b of FIG. 4A is the photoelectric conversion layer 103c of FIG. 4B. In this case, the first layer 104a of FIG. 4A corresponds to 104c of FIG. 4B, and the second layer 105 of FIG. 4A corresponds to 105c of FIG. 4B. The third layer 106b in FIG. 4A corresponds to the third layer 106c in FIG. 4B.

(Photoelectric conversion layer)
As shown in FIG. 4A, the photoelectric conversion layer 103b is mainly composed of a plurality of particles (that is, particles of the inorganic semiconductor) 20 containing an inorganic semiconductor as a main component or an aggregate or a thin film thereof. A second layer 105 having a layer 104a, formed on the surface of the first layer 104a, containing a perovskite structure as a main component, and further composed of an aggregate or a thin film (complex) containing the core-shell particles 10, and an organic substance. It is preferable that the third layer 106b composed of a plurality of particles containing a metal complex as a main component or an aggregate thereof or a thin film is laminated. Here, "containing an organometallic complex as a main component" means that the content of the organometallic complex is more than 50% by volume in the particles, their aggregates, or the thin film. It is preferably more than 90% by volume, and more preferably substantially composed of an inorganic semiconductor. That is, the photoelectric conversion layer 103b is arranged in the order of the positive electrode layer 101, the third layer 106b, the second layer 105, the first layer 104, and the negative electrode layer 102, and at least a current path from the positive electrode layer 101 to the negative electrode layer 102 is formed. It should be configured so as to. The larger the number of current paths formed, the more preferable, but the adjacent current paths may or may not be electrically connected to each other.

Further, regarding the materials and compositions of the three layers 104 to 106b, the energy levels of the conduction bands (LUMO, excited state) are higher in the order of the first layer 104, the second layer 105, and the third layer 106b, and the second layer. The energy level of the valence band (HOMO, ground state) of the layer is determined to be higher than the energy level of the valence band of the third layer 106b. In the conduction band, the energy level of the second layer 105 is higher than the energy level of the first layer 104, and the energy level of the third layer 106b is higher than the energy level of the second layer 105. For example, for the first layer 104, the energy level of the valence band can be -8 eV or more, and the energy level of the conduction band can be -4 eV or less. At this time, for the second layer 105, the energy level of the valence band can be set to −5.5 eV or more, and the energy level of the conduction band can be set to -3 eV or less. Further, for the third layer 106b, it is preferable that the energy level of the valence band is −6 eV or more and the energy level of the conduction band is −2 eV or less.

The third layer 106b is a thin film that covers the surface (exposed surface) of the molecules of the perovskite structure contained in the second layer among the photoelectric conversion element precursors composed of the first layer 104 and the second layer 105. It is good. The molecule of the organic metal complex constituting the third layer 106b is obtained by coordinate-bonding an inorganic transition metal and an organic ligand. Here, 106A represents the inorganic transition metal ion of the third layer 106b, and 106B represents the organic ligand of the third layer 106b.

In the organometallic complex, the inorganic transition metal ion is preferably localized on the second layer side in a film form so as to be directly bonded to the perovskite structure of the second layer 105. On the other hand, the organic ligand is preferably localized on the opposite side (positive electrode side) of the second layer in a film form. Then, in order to realize the amplification of the photocurrent described later, the molecules of the organic metal complex are arranged in the order of the organic ligand and the inorganic transition metal ion in the current path from the positive electrode layer 101 side to the second layer 105 side. As described above, it is preferable that the molecule of the perovskite structure is bound to the molecule. That is, it is divided into a layer composed of inorganic transition metal ions and a layer composed of organic ligand ions. The boundary between the two layers can be confirmed by using, for example, a transmission electron microscope (TEM).

Examples of the inorganic transition metal ion here include Eu ³⁺ and Cr ^{3+ having a reduction level of LUMO, and Ru 2+} , Fe ²⁺ , Mn ²⁺ , and Co ²⁺ having an oxidation level of HOMO. Further, as the organic ligand here, a ligand of a general metal complex, for example, (i) a carboxyl group, a nitro group, a sulfo group, a phosphate group, a hydroxy group, an oxo group, an amino group and the like can be used. Organic compounds possessed; (ii) ethylenediamine derivatives; (iii) ring heteroatom-containing organic ligands such as terpyridine derivatives, phenanthroline derivatives, bipyridine derivatives; (iv) catechol derivatives, quinone derivatives, naphthoic acid derivatives, acetylacetonate derivatives (iv) Specifically, for example, an acetylacetonate-based organic ligand such as acetylacetone (here, the "acetylacetonate-based organic ligand" is a large number of transition metal ions via two oxygen atoms (for example,). It means an organic ligand capable of coordination bond (while forming a six-membered ring)) and the like. The terpyridine derivative has a composition represented by the following formula (1).

The thickness of the third layer 106b is preferably, for example, about 1 nm or more and 10 nm or less. If the third layer 106b is thicker than 10 nm, the energy barrier becomes too thick to obtain a sufficient tunnel probability, and the amplification of the photocurrent in the photoelectric conversion layer 103b is hindered. Further, if the third layer 106b is thinner than 1 nm, the light is not irradiated and the tunnel current flows even when the band is not bent, so that the photodetection function of the photoelectric conversion layer 103b becomes meaningless.

A photoelectric conversion element formed by laminating a second layer 105 composed of a composite of core-shell particles 10 and a perovskite structure and a third layer 106b composed of an aggregate or a thin film containing an organometallic complex as a main component. The light receiving member can be used as a photoelectric conversion element by being provided between the hole transport layer and the electron transport layer.

(Energy band structure)
5 (a) to 5 (d) show the structure of the energy band of each layer during the operation of the photoelectric conversion element 100 according to the present embodiment. Here, 106A represents the inorganic transition metal ion of the third layer 106b, and 106B represents the organic ligand of the third layer 106b.

In the non-irradiated state, the energy level of the conduction band of the third layer 106b is higher on the positive electrode layer 101 side than the Fermi level of the positive electrode layer 101, as shown in FIG. 5 (a). , The current from the positive electrode layer 101 to the negative electrode layer 102 is blocked.

When light L ₁ to the photoelectric conversion element having a wavelength of more than 800nm is irradiated, the core of the core-shell particles 10 constituting the second layer 105 (inorganic nanoparticles 11), absorbs the light, the wavelength in the visible light Convert. The perovskite structure absorbs the wavelength-converted light to generate electrons e and holes h, the electrons e _{move to the conduction band E c2} , and the holes h _{move to the valence band E v2} (FIG. 5 (b). )).

_{At this time, since the energy levels E c1} , E _c2 , and E _{c3 in} the conduction bands of the first layer 104a, the second layer 105, and the third layer 106b are in _{the relationship of E c3} > E _c2 > E _c1 , the second layer. The electrons e generated in the layer 105 and transferred to the conduction band of the same layer are transferred to the conduction band E _c1 of the first layer 104a, which is in a lower energy state.
_{On the other hand, the energy levels E v1} , E _v2 , and E _v3 of the valence band of the first layer 104a, the second layer 105, and the third layer 106b are E _v2 > E _v1 layer and E _v2 > E _v3 . Therefore, as shown in FIG. 5 (c), the holes generated in the second layer and transferred to the valence band are relatively high (low for holes) as compared with the first and third layers. It is trapped in the valence band of the second layer, which is in the energy state.

Due to the influence of holes that are trapped and concentrated and distributed (positive potential), the potential energy of electrons decreases in the vicinity of the valence band of the second layer, and the energy level of the conduction band decreases. .. Since the energy level of the conduction band decreases as it is closer to the second layer in which holes are trapped, the energy level of the conduction band of the third layer is lower on the second layer side and on the positive electrode layer side. It has a sharp shape. Therefore, for the electrons existing in the positive electrode layer 101, the energy barrier of the third layer becomes thin, and as shown in FIG. 5D, it becomes possible to tunnel to the negative electrode layer side. That is, when the photoelectric conversion element is irradiated with light, a large number of electrons on the positive electrode side (electrons in a state where the light is not irradiated) blocked by the energy barrier of the third layer are tunneled through the thinned energy barrier. It can be (permeated) and flow into the negative electrode side. Therefore, the photoelectric conversion element of this modification can realize a large amplification of the current directly generated by the irradiated light.

(Manufacturing method of core-shell particles)
Next, a method for producing the core-shell particles 10 of the present disclosure will be described. The method for producing the core-shell particles 10 of the present disclosure includes an inorganic nanoparticle synthesis step and a coating layer forming step.

"Inorganic nanoparticle synthesis process"
In the inorganic nanoparticle synthesis step, the inorganic nanoparticles 11 are synthesized. The method for synthesizing the inorganic nanoparticles 11 is not particularly limited, and examples thereof include a precipitation method and a hydrothermal synthesis method. Specifically, as the main raw material, Ln (lanthanoid) oxides, _{e.g., Er 2 O 3, Tm 2} O 3, Ho 2 O 3, Yb 2 O 3 or Ln halide, for _example, ErCl 3, ErF ₃ , TmCl ₃ , TmF ₃ , HoCl ₃ , HoF _3, etc. are used to synthesize trifluoroacetate. Further, sodium trifluoroacetate and a chain organic molecule are used, and the reaction is carried out under high temperature conditions (100 to 400 ° C.) under _{an N 2 or Ar atmosphere.} Inorganic nanoparticles 11 are obtained by cooling the solution after the reaction, adding an organic solvent such as ethanol if necessary, and then centrifuging to separate the inorganic nanoparticles 11.

"Coating layer forming process"
Next, in the coating layer forming step, the coating layer 12 is formed on the inorganic nanoparticles 11 obtained in the inorganic nanoparticles synthesis step. The method for forming the coating layer 12 is not particularly limited, and examples thereof include a precipitation method and a hydrothermal synthesis method. Specifically, for example, the inorganic nanoparticles 11 are reacted with a solution containing cesium oleate synthesized from cesium carbonate and lead halide (PbX _2). The temperature is 120 to 200 ° C. and the atmosphere is nitrogen. The solution after the reaction is cooled and the fine particles are separated by centrifugation. Core-shell particles can be obtained by firing the separated fine particles (for example, 200 ° C. to 300 ° C.).

(Manufacturing method of photoelectric conversion element)
6 (a) to 6 (e) are cross-sectional views of the object to be processed in the manufacturing process of the photoelectric conversion element 100. The photoelectric conversion element 100 can be manufactured mainly by the following procedure.

First, as shown in FIG. 6A, a base material provided with the negative electrode layer 102 for forming the photoelectric conversion layer 103 is prepared. As the negative electrode layer 102 on the base material, an electrode member that functions as a negative electrode layer and has transparent conductivity is used. Here, the case where the buffer layer 107 is formed on one surface of the negative electrode layer 102 is illustrated, but the buffer layer 107 may not be formed. The buffer layer 107 functions as an electron transport layer or a hole blocking layer. The buffer layer 107 can be formed by applying a solution of a material to the negative electrode layer 102 by using a spin coating method or the like, and heating (drying) the solution. This heating may be performed, for example, at about 120 to 450 ° C. for about 10 to 60 minutes. The material coating conditions (coating time, etc.) may be adjusted so that the thickness of the buffer layer 107 is, for example, about 1 to 100 nm.

Next, as shown in FIG. 6B, a plurality of particles containing an inorganic semiconductor as a main component (that is, an inorganic semiconductor) on one surface side of the negative electrode layer 102 (sandwiching the buffer layer 107 if it is present). Particles) 20 to form the first layer 104a. The first layer 104a can also be formed by applying a solution of the material and heating it, similarly to the buffer layer 107. This heating may also be performed, for example, at about 120 to 450 ° C. for about 10 to 60 minutes. The material coating conditions (coating time, etc.) may be adjusted so that the thickness of the first layer 104a is, for example, about 10 to 1000 nm, preferably about 50 to 500 nm.

Next, as shown in FIG. 6C, the surface of the particles 20 of the inorganic semiconductor contains the raw material of the perovskite structure as the main component and the core-shell particles 10 by using a spin coating method, a dip method, or the like. The second layer 105 may be formed by applying a solution to be coated and heating it. This heating may be performed, for example, at about 40 to 100 ° C. for about 5 to 10 minutes. The thickness of the second layer 105 is adjusted according to the material coating conditions (coating time, etc.). By using a material in a liquid state, a thin film can be formed under conditions having a smaller environmental load than in the case of using an inorganic semi-material in a solid state such as silicon.

Next, as shown in FIG. 6 (d), the third layer 106 may be formed on the second layer 105. More specifically, by using a spin coating method, a dip method, or the like, a material containing a p-type organic semiconductor or an inorganic semiconductor as a main component is vapor-deposited or a solution of the material is applied onto the second layer 105. It is preferable to form the three layers 106. In reality, when the second layer 105 is formed, the gaps between the particles 20 of the inorganic semiconductors of the first layer 104a are almost filled. Therefore, the third layer 106 can be formed in a film shape mainly on the exposed portion of the surface of the second layer 105 on the positive electrode layer 101 side (opposite to the negative electrode layer 102).

When forming an organometallic complex as the third layer (that is, when forming the third layer 106b), the application and heating of the solution here may be performed in two steps. That is, in the first step, a solution of an inorganic transition metal such as europium may be applied and heated, and then in the second step, a solution of an organic ligand such as terpyridine may be applied and heated. As a result of forming the third layer 106b in two stages in this way, the third layer 106b is composed of a layer 106A made of an inorganic transition metal and a layer made of an organic ligand in order from the second layer 105 side. It has a structure in which 106B, is laminated.

Finally, as shown in FIG. 6E, the photoelectric conversion element 100 of the present embodiment is formed by forming an electrode member (positive electrode layer) 101 that functions as a positive electrode and has conductivity on the third layer 106. Can be obtained.

In the above-mentioned method for manufacturing the photoelectric conversion element, the case where the porous first layer 104a is used has been described, but the layered first layer 104b can also be manufactured by the same method as above. The first layer 104b can be formed by a known method such as thin film deposition.

As described above, in the core-shell particles 10 of the present embodiment, the long-wavelength light such as near-infrared light absorbed by the core inorganic nanoparticles 11 is converted into short-wavelength light such as visible light and ultraviolet light. The converted light is reabsorbed by the inorganic perovskite-type material of the coating layer 12 serving as a shell and converted into electric power. Therefore, according to the core-shell particles 10 of the present embodiment, it is possible to generate photoelectric conversion or electromotive force from light having a long wavelength, which was difficult in the past.

Further, the core-shell particles 10 of the present embodiment have a core-shell structure, so that energy transfer between close inorganic nanoparticles and an inorganic perovskite-type substance can be reliably and efficiently performed, and energy loss can be reduced. Therefore, even if the light absorbed by the core is weak light, excellent photosensitization characteristics can be realized.

Hereinafter, the effects of the present invention will be made clearer by the examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

(Manufacturing of core shell particles)
In line with the above-mentioned method for producing core-shell particles, specifically, core-shell particles were produced under the following conditions.

(Core shell particle 1)
Inorganic nanoparticles, which are the core of core-shell particles, were synthesized by the precipitation method. Specifically, 1 mmol of Er oxide (Er ₂ O ₃ ) was dissolved in 5 mL of trifluoroacetic acid and 5 mL of water, and the mixture was heated and stirred at 80 ° C. under reduced pressure. _{2.5 mmol of sodium trifluoroacetate (NaCOOCF 3} ) was added to the powder obtained by evaporation to dryness, and the mixture was dissolved in 15 mL of oleylamine. After stirring at 100 ° C. for 30 minutes under reduced pressure, nitrogen was introduced into the system, and the mixture was stirred at 330 ° C. for 1 hour. After cooling to 80 ° C., ethanol 20mL was added to separate the NaErF ₄ nanoparticles by centrifugation.

0.81 g of cesium carbonate ( _{CsCO 3} ) was dissolved in 2.5 mL of oleic acid and 40 mL of octadecene, and the mixture was stirred at 120 ° C. for 1 hour under a nitrogen atmosphere. Further, the mixture was stirred at 160 ° C. for 30 minutes to obtain cesium oleate.

Formation of the coating layer to NaErF ₄ nanoparticles synthesized above was carried out by precipitation. Specifically, 0.4 mmol of _{PbBr 2 and NaErF 4} nanoparticles were dispersed in 10 mL of octadecene, and the mixture was stirred at 120 ° C. for 1 hour under a nitrogen atmosphere. Further, 1 mL of oleic acid and oleylamine were added. After raising the temperature to 180-190 ° C., 0.85 mL of cesium oleate was added and the mixture was stirred for 1 hour. After cooling, the nanoparticles were separated by centrifugation and calcined at 200 ° C. for 30 minutes to obtain one layer of core-shell particles (particle size 25 nm). The particle size of the core-shell particles was obtained from the SEM image obtained from the SEM observation.

(Core shell particles 2)
PbBr ₂ 0.4 mmol and the one-layer core-shell particles obtained above were dispersed in 10 mL of octadecene, and the mixture was stirred at 120 ° C. for 1 hour under a nitrogen atmosphere. Further, 1 mL of oleic acid and oleylamine were added. After raising the temperature to 180-190 ° C., 0.85 mL of cesium oleate was added and the mixture was stirred for 1 hour. After cooling, the nanoparticles were separated by centrifugation and calcined at 200 ° C. for 30 minutes to obtain two layers of core-shell particles (particle size 30 nm).

(Nanoparticle 1)
Inorganic nanoparticles were synthesized by the precipitation method. Specifically, 1 mmol of Er oxide (Er ₂ O ₃ ) was dissolved in 5 mL of trifluoroacetic acid and 5 mL of water, and the mixture was heated and stirred at 80 ° C. under reduced pressure. _{2.5 mmol of sodium trifluoroacetate (NaCOOCF 3} ) was added to the powder obtained by evaporation to dryness, and the mixture was dissolved in 15 mL of oleylamine. After stirring at 100 ° C. for 30 minutes under reduced pressure, nitrogen was introduced into the system, and the mixture was stirred at 330 ° C. for 1 hour. After cooling to 80 ° C., ethanol 20mL was added to separate the NaErF ₄ nanoparticles (particle size 20 nm) by centrifugation.

Specifically, the photoelectric conversion element was manufactured under the following conditions in accordance with the above-mentioned manufacturing method of the photoelectric conversion element.

(Example 1)
As a member provided on the substrate and used as a negative electrode layer, a member substantially made of antimony-doped indim (ATO) was prepared. To one surface of the member, ethanol _{(C 2} H 5 OH) solution 200μl containing 10mM concentration of europium chloride hydrate _{(EuCl 3 · 6H 2 O)} , was spin coated at a rotational speed of 3000 rpm. Subsequently, the spin-coated mixed solution was heated at 120 ° C. for 10 minutes and then at 450 ° C. for 1 hour in order to form a buffer layer _{substantially composed of europium oxide (Eu 2} O _3).

Next, 120 μl of a mixed solution containing titanium oxide (TiO ₂ ) paste (PST18NR, manufactured by JGC Catalysts and Chemicals Co., Ltd.) and ethanol at a weight ratio of 1: 3.5 was spun on the buffer layer at a rotation speed of 6000 rpm. Coated. Subsequently, the spin-coated mixed solution was heated at 120 ° C. for 10 minutes and then at 450 ° C. for 1 hour in order to obtain a first layer (porous film) composed of a plurality of particles substantially made of titanium oxide. Formed.

Next, with respect to the porous film of the first layer, lead iodide (PbI ₂ ) was 1M, cesium iodide (CsI) was 1M, and core-shell particles 1 were 8% by weight (w%) at a concentration of 0.5M or less. ), 100 μl of a mixed solution of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) was spin-coated at a rotation speed of 5000 rpm. Subsequently, the spin-coated mixed solution was heated at 185 ° C. for 15 minutes to form a second layer containing the core-shell particles of the present invention.

Next, 100 μl of an isopropyl alcohol (IPA) solution containing europium chloride (EuCl _{3) at a concentration of 5 mM was spin-coated on the second layer at a rotation speed of 5000 rpm.} Subsequently, the spin-coated mixed solution was heated at 100 ° C. for 15 minutes to form a layer substantially composed of europium.

Next, 200 μl of an isopropyl alcohol (IPA) solution containing terpyridine (2,2': 6', 2 "-terpyridine) at a concentration of 20 mM was held for 30 seconds with respect to this layer containing europium as a main component, and then at 3000 rpm. Spin-coated at rotation speed. Subsequently, the spin-coated mixture was heated at 100 ° C. for 15 minutes to form a layer substantially composed of terpyridine.

Finally, the positive electrode layer (Ag) is formed (deposited) on the opposite side of the negative electrode layer and in contact with the third layer with the laminate composed of the first layer, the second layer, and the third layer sandwiched between them. The photoelectric conversion element of Example 1 was manufactured.

(Example 2)
A photoelectric conversion element was manufactured under the same conditions as in Example 1 except that the core-shell particles 2 were used instead of the core-shell particles 1.

(Example 3)
A photoelectric conversion element was manufactured under the same conditions as in Example 1 except that a layer made of BCP (thickness: 30 nm) was formed as the third layer by a vacuum vapor deposition method.

(Example 4)
A photoelectric conversion element was manufactured under the same conditions as in Example 1 except that a layer (thickness 100 nm) substantially composed of Spiro-OMeTAD was formed as the third layer.

(Comparative Example 1)
A photoelectric conversion element was manufactured under the same conditions as in Example 1 except that nanoparticles 1 were used instead of core-shell particles 1.

(Emission spectrum of core-shell particles)
The spectra of the core- shell particles 1 and 2 and the nanoparticles 1 when irradiated with near-infrared light having a wavelength of 980 nm were measured with an absolute PL quantum yield measuring device manufactured by Hamamatsu Photonics.

(Light absorption spectrum of core-shell particles)
The light absorption spectrum of the core-shell particles 2 was measured with an absolute PL quantum yield measuring device manufactured by Hamamatsu Photonics.

(SEM observation)
A cross section of the photoelectric conversion element of Example 2 was observed at a magnification of 150,000 times using a scanning electron microscope manufactured by Hitachi High-Technologies Corporation, and an SEM image was obtained.

(Response characteristics of photocurrent)
The optical response characteristics were measured with respect to Example 2. The voltage applied between the positive electrode layer and the negative electrode layer of the photoelectric conversion element was set to −0.5 V. The wavelength and irradiance of the light irradiating the photoelectric conversion element were set to 808 nm and 10 mW / cm ² , respectively.

FIG. 7 is a graph showing the spectrum of the light wavelength-converted by irradiating the photoelectric conversion elements of the core- shell particles 1 and 2 with near-infrared light having a wavelength of 980 nm. The horizontal axis of the graph indicates the wavelength (nm), and the vertical axis of the graph indicates the intensity (Counts / s). Since the peaks are shown at three wavelengths (around 550 nm, about 650 nm, and about 800 nm), it can be seen that the irradiated near-infrared light is converted into these three wavelengths. The broken line shows the spectrum when the coating layer CsPbBr ₃ is two layers (core-shell particles 2), and the dotted line _{shows the spectrum when the coating layer CsPbBr 3} is one layer (core-shell particles 1). For comparison, the spectrum of only NaErF4 (solid line) of the nanoparticles 1 is also shown. The emission intensity is _{remarkably increased by the coating layer CsPbBr 3} , and further increased by increasing the thickness of the layer. This is a result showing _{that the coating layer CsPbBr 3} suppresses the deactivation, whereas the light emission is deactivated by the thermal vibration of the chain organic molecule in the case of only the inorganic nanoparticles. The position of the peak can be adjusted by changing the material, shape, size, etc. of the core-shell particles.

FIG. 8 is a graph showing the change in absorption rate due to the difference in the structure of the core-shell particles in the second layer. The horizontal axis of the graph indicates the wavelength (nm), and the vertical axis of the graph indicates the intensity (Counts / s). The solid line shows the result of the core-shell particle 2. For comparison, the absorption rate (dashed line) of the nanoparticles of _{NaYF 4} containing 2% of Er ions is also shown. Since the core-shell particles 2 contain 100% of Er ions, the intensity of the irradiated near-infrared light is about one-seventh lower than that of general up-conversion nanoparticles (using 2% of Er). It has become. It is considered that the near-infrared light corresponding to the lowered intensity is absorbed by the core (inorganic nanoparticles) of the core-shell particles.

FIG. 9 is an SEM image of a cross section of the photoelectric conversion element manufactured as an example. It can be seen that a structure in which layers consisting of a first layer, a second layer, and a third layer are laminated in order is formed, and a current path connecting the Ag and ATO electrodes is formed.

FIG. 10 is a graph showing the spectrum of the light wavelength-converted by irradiating the second layer of the photoelectric conversion element of Example 2 with near-infrared light having a wavelength of 980 nm. The horizontal axis of the graph indicates the wavelength (nm), and the vertical axis of the graph indicates the intensity (Counts / s). Originally, the perovskite layer (here, CsPbI ₃ ) cannot absorb light of 800 nm or more, but in the second layer of Example 2, the light of 980 nm is shown in FIG. 7 by containing the core-shell particles 2. It can be converted to visible light. _{Since light emission derived from CsPbI 3} was observed near 700 nm, it is shown _{that CsPbI 3} absorbed the visible light wavelength-converted by the core-shell particles 2.

FIG. 11 is a graph showing the response speed of the photocurrent obtained by irradiating the photoelectric conversion element of Example 2 with light at a predetermined timing. The horizontal axis of the graph shows the elapsed time (s), and the vertical axis of the graph shows the photocurrent (A / cm ² ). The photocurrent shows an instantaneous rise and fall according to the on / off of the voltage, and it can be seen that a sufficient response speed can be realized. The photoelectric conversion efficiency was 75% and the sensitivity was 0.49 A / W.

10 ... Core-shell particles 11 ... Inorganic nanoparticles 11a ... Particle size of inorganic nanoparticles 12 ... Coating layer 12a ... Coating layer thickness 100 ... Photoelectric conversion element 101 ... Positive electrode layer 102 ... Negative electrode layer 103 ... Photoelectric conversion layer 104 ... First layer 105 ... Second layer 106 ... Third layer 107 ... Buffer layer

Claims (7)

1. Inorganic nanoparticles with wavelength conversion capability of light,
   A core-shell particle having a core-shell structure, comprising a coating layer formed on the surface of the inorganic nanoparticles and made of an inorganic perovskite-type substance.
2. The core-shell particle according to claim 1, wherein the inorganic nanoparticles contain a rare earth element.
3. A complex characterized by being an aggregate or a thin film containing a perovskite structure as a main component and further containing the core-shell particles according to any one of claims 1 or 2.
4. The layer composed of the complex according to claim 3 and
   A light receiving member for a photoelectric conversion element, which is formed by laminating a layer composed of an aggregate or a thin film containing an organic or inorganic semiconductor (including a metal complex) as a main component.
5. A photoelectric conversion element provided with the light receiving member for the photoelectric conversion element according to claim 4 between the hole transport layer and the electron transport layer.
6. A first layer composed of a plurality of particles containing an inorganic semiconductor as a main component or an aggregate or a thin film thereof,
   A second layer formed on the surface of the first layer and composed of the complex according to claim 3,
   A third layer composed of a plurality of particles or aggregates thereof containing an organic or inorganic semiconductor (including a metal complex) as a main component, or a thin film.
   Are stacked in order,
   In the conduction band, the energy level of the second layer is higher than the energy level of the first layer, and the energy level of the third layer is higher than the energy level of the second layer.
   A photoelectric conversion element characterized by this.
7. The photoelectric of claim 6, wherein the third layer contains an organic metal complex as a main component, and the energy level of the second layer in the valence band is higher than the energy level of the third layer. Conversion element.

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